1. Field of the Invention
The present invention concerns a jaw palletizer for the graphics industry.
2. Description of Related Art
In the graphics industry, the sheets coming off the rotary press are fed in the form of a stream of sheets overlapping like scales into a stacker, where up to a pre-set number of sheets are assembled in superposed layers to form a bundle. This can, for example, be between 80 and 120 cm in height. The bundle is then conveyed on roller tables to a binding station, from where it is transported onto a pallet for the sheets to be given further handling elsewhere.
Jaw palletizers are known for conveying bundles onto pallets which comprise a jaw with movable cheeks supported by a winch housed on a trolley moving along overhead rails, the jaw being additionally equipped with guide elements in the form of movable vertical rods in guides interposed between said trolley and its axles, which support the wheels moving along the overhead rails. This design type is to be found in British patent no. 2,119,340 in which one of the cheeks of the jaw is a fixed part of its structure, whilst the other is attached to the moving part of a cylinder/piston unit to enable bundles of varying lengths to be gripped. With palletizers of this type, however, the support given to the bundle is unbalanced, with the result that the guide rods are subjected to notable stresses and strains. These rods can be of considerable lengths, since they must be able to form on the pallet a pile of different superposed layers of bundles and, furthermore, the overhead rails need to be positioned at a certain height so as not to obstruct the free passage of people, fork-lift trucks and other vehicles. It must also be pointed out that jaws of this type, with the addition of the bundle being carried, often make for a notable weight, in the region of 150 kg, for example. This type of design can accordingly cause the bundle to oscillate during con veyance. To avoid this oscillation, which could seriously affect the formation of a compact pile on the pallet, the bundle would have to be transported at low speed. Another disadvantageous feature of the palletizer disclosed in the British patent 2,119,340 is that the bundles, after being picked up, have to be transported in the same position as that in which they were collected. To permit conveyance of bundles that are of a fair height, jaws of this type employ cylinder/piston units of considerable length. Apart from having unfavorable repercussions so far as the balance of the combined jaw/bundle unit is concerned, this also has a negative effect on production costs, since such lengthy cylinder/piston units are very expensive. They also, in proportion with the length of the respective bundle, occupy a good deal of space. U.S. Pat. No. 4.256.429 discloses a jaw for conveying sheet bundles that is of the same type as the one described above, but provision is made for it to be used suspended by means of a chain with a conveyor device. Provision is also made, with this type of jaw, for the bundle gripped between the cheeks to be rotated lengthwise. For this purpose, rotatable, disc-shaped supports are attached to the cheeks, one of them being connected by chain transmission to a motor mounted on the top of the transverse part of the jaw. The said transverse part is also provided with a vertical cylinder/piston unit with a catch projection for ensuring that the bundle is supported at the correct height level, to allow enough room for it to rotate freely. This device however, in which a cylinder/piston unit is also used, carries the same disadvantages as those already mentioned. In this device, in fact, there are no guide rods in the vertical plane, so that in the course of conveyance, which is manually controlled by an operator, the jaw and the bundle in its grip are able to oscillate freely. In this case, too, conveyance speeds are low.
A jaw palletizer for conveying sheet bundles is also known from Italian patent no. 1,020,747, comprising two opposed cylinder/piston units, rod-shaped vertical elements serving as guides, and a vertical cylinder/piston unit whereby the jaw is attached to a trolley that moves on overhead rails. In palletizers of this type the cylinder/piston units are controlled independently, so that there can be no certainty that when the bundle is picked up the actions will be precisely opposed. These palletizers also have the disadvantage that bundles are liable to oscillate while being conveyed. The way they are designed also necessitates numerous components which raise their price considerably. In view of the weights, already referred to, of the jaws and the respective bundles, the jaw's cylinder/piston support is clearly incapable of speedily effecting vertical lifts of sufficient precision to ensure that the piles of bundles formed on the pallet are automatically compact.
Not only do all the known designs of jaw palletizers fail to pick up the bundle exactly in the center, they all share the disadvantage of not allowing for the rotation of the jaw in the horizontal plane.
With these known types of jaw, the bundles can therefore only be arranged on the pallets in a formation where they are parallel with one another, which means that really compact piles with "self-secured" bundles cannot be obtained, which is of course desirable.